Abstract:

An optoelectronics chip-to-chip interconnects system is provided,
including at least one packaged chip to be connected on the
printed-circuit-board with at least one other packaged chip,
optical-electrical (O-E) conversion mean, waveguide-board, and (PCB).
Single to multiple chips interconnects can be interconnected provided
using the technique disclosed in this invention. The packaged chip
includes semiconductor die and its package based on the ball-grid array
or chip-scale-package. The O-E board includes the optoelectronics
components and multiple electrical contacts on both sides of the O-E
substrate. The waveguide board includes the electrical conductor
transferring the signal from O-E board to PCB and the flex optical
waveguide easily stackable onto the PCB to guide optical signal from one
chip-to-other chip. Alternatively, the electrode can be directly
connected to the PCB instead of including in the waveguide board. The
chip-to-chip interconnections system is pin-free and compatible with the
PCB. The main advantages of this invention are to use the packaged chip
for interconnection and the conventional PCB technology can be used for
low speed electrical signal connection. Also, the part of the heat from
the packaged chip can be transmitted to the PCB through the conductors,
so that complex cooling system can be avoided.

Claims:

1. A waveguide board of optical interconnects system comprising:at least
one substrate; andat least one flex optical circuit for transmitting and
receiving chip-to-chip optical signals, comprising at least one optical
waveguide;wherein each said optical waveguide comprises a 45-degree
mirror at each end of said waveguide to redirect light beams.

2. The system of claim 1, further comprising:at least one external
electrode at one end or at both ends of the circuit;at least one O-E
board; anda PCB;wherein said external electrode electrically connects
with said O-E board and said PCB.

3. The system according to claim 2, wherein said external electrodes have
contacts located on the top and bottom surfaces of said waveguide board,
wherein said contacts provide connections for power, ground, cooling,
and/or low-speed electrical signals.

4. The system of claim 1, wherein said at least one substrate comprises an
electrically-insulating flexible material which can act as under-cladding
for said waveguide board.

5. The system of claim 1, wherein said substrate comprises Si, SiC, a
ceramic material, or a polymer including polyamide, polyester, epoxy,
urethane, polystyrene, or polycarbonate.

6. The waveguide board of claim 1, wherein said at least one substrate is
rigid or flexible.

7. The waveguide board of claim 1, wherein material of said optical
waveguide made from polymer-based material, which can be a fluorine-based
polymer, PMMA or a PMMA-based material, or epoxy resin.

8. The waveguide board of claim 1, further comprising a defractive or
reflective microlens above the mirror for collimating or focusing light
beams, wherein the microlens can be a concave lens, a grating lens, or a
planar lens.

9. The waveguide board of claim 1, further comprising a layer of epoxy
resin.

10. A method for fabricating the waveguide board of optical interconnect
system, comprising:forming a core layer on the first substrate using
spin-coating or standard deposition techniques including sputtering,
evaporation polymerization, or vapor-phase
polymerization;photolithography-based patterning and subsequent etching
on said core layer using ECR, RIBE, or milling to form at least one
core;formation of a clad layer; andetching for the 45-degree mirrors
using direct cutting techniques including laser drilling or knife-cutting
methods

11. The method of claim 10, wherein said etching for said 45-degree
mirrors is done using laser drilling, wherein the laser beam can be
positioned at a 45-degree angle with respect to the horizontal to said
first substrate or said first substrate can be inclined at a 45-degree
angle with respect to the laser beam.

12. The method of claim 10, wherein said etching for said 45-degree
mirrors is done using direct cutting with a diamond blade, wherein either
the blade or the first substrate is moved at a 45-degree angle.

13. The method of claim 10, wherein said etching for forming said
45-degree mirrors is done using direct cutting with a 90-degree V-shaped
diamond blade.

14. The method of claim 10, further comprising depositing a reflective
metal on the etched-out surfaces for the 45-degree mirrors using standard
deposition techniques, wherein said standard deposition technique can
comprise sputtering, thermal evaporation, coating, ion-beam evaporation,
or CVD, wherein said reflective metal can be gold, aluminum, copper,
tungsten, chromium, or platinum.

15. The method of claim 10, further comprising forming the electrodes
using standard photolithography-based patterning, etching, and
metallization, wherein RIE, ECR-RIBE, or milling is used for etching, and
laser drilling is used to make via-holes for the electrodes.

16. The method of claim 10, wherein the metallization is a two-step
metallization process comprising:metallization to form the electrodes
prior to the deposition of the core layer; andmetallization after forming
the waveguides.

17. The method of claim 10, further comprising hardening the
under-cladding of claim 4 or 13 using UV- or heat-based curing
techniques.

18. The method of claim 10, further comprising forming an epoxy-resin
layer on the first substrate.

19. The method of claim 10, further comprising forming the microlens on
said epoxy-resin layer.

20. The method of claim 10, further comprising polishing the core layer to
an adequate thickness appropriate for the core layer to guide the light
beam using chemical or mechanical polishing.

21. The method of claim 10, further comprising independently forming the
concave lens, grating lens, or planar lens and bonding said lens onto the
mirror using epoxy resin.

[0003]This invention relates to chip-to-chip interconnection, and more
particularly to, connecting signal line of single processor or
multiprocessor chips to signal line of single or multi memory chips which
are used in all kinds of computers covering from personnel computer to
super-computer, and also in game system.

BACKGROUND OF THE INVENTION

[0004]The increasing of higher level of integration within electrical
integrated circuit (IC) leads to both higher data rates and larger number
of IC interconnections. Today, the inherent signal speed of IC is
increased to 3 GHz, and shortly it will be reached to over 10 GHz. The
number of pin connection is also increased, with single IC requiring
close to 2000 interconnection (i.e. single processor), and shortly it
will be increased to over 5000. Simultaneously achieving higher data
rates and higher interconnect densities within the higher level of
packaging, covering from die-level packaging to chip-to-chip (hereafter
chip indicates the die with package) interconnection on the printed
circuit board (PCB), will be increasingly difficult as the IC
technologies continue to evolve increasing the signal speed and
interconnection number.

[0005]With increasing of the signal speed and interconnection number
within the IC, low-cost high-level packaging and related interconnection
technology after post packaging are highly desirable to make available in
consumer level. The packaging technology especially for single chip
package (also mentioned as packaged-chip in the text) is improved to
tackle the signal speed and pin connections. Ball grid array (BGA), chip
scale package (CSP) etc. for IC package are developed accommodating
required pin connections and the signal speeds, and it can accommodate
the on-chip (inside the chip) speed. However, when it comes to the case
of chip-to-chip (off-chip) connection on the PCB, the transition from
thin film technology (which is IC and packaging technology) to the thick
film technology of the PCB is a primarily dramatic transition. This is
not only in terms of the technology but also in terms of interconnection
density achievable on the single layer. With increasing of on-chip signal
speed, the off-chip signal speed also increases. This off-chip electrical
signal creates noises such as reflection caused by poor shapes of
electrical interconnects, connecting the inter chip, or the influence of
the cross-talk. In addition, the high-speed signal creates also high
frequency electromagnetic waves from the electric interconnect to
adversely affects the peripheral circuits. To reduce this reflection loss
transmission line is to be properly designed with the proper
characteristic impedance through out the inter-chip signal line with
minimal discontinuities. To suppress the electromagnetic affect on the
neighboring circuit, proper signal line and shielding in the PCB is to be
designed. In the case of high speed off-chip interconnects especially
over 3 GHz where line length is long, both reducing reflection loss and
also suppressing electromagnetic interference are practically challenging
in some extent, and are not cost-effective to implement by using of
conventional PCB technology. Today's off-chip electrical interconnects
are being implementing by lowering the signal speed at the level where
conventional PCB technology is used and no such problems are occurred. In
this case, the fully integration technology within IC in other words, the
intra chip signal speed is not fully utilized.

[0006]FIG. 1 shows the schematic representing the conventional
chip-to-chip interconnection on the conventional PCB 100. Here, chip 120
(for example processor) is connected with chip 130 (for example 3) by
multilayered electrical signal lines 110 in the PCB 1. FIG. 2 shows the
schematic representing the conventional BGA (ball grid array) and CSP
(chip-scaled package) based packaging for high-speed single chip package
(for example processor). In both type of packagings, die 122 and die 132
are attached with the ceramic or polymer substrate 124 and 134,
respectively, containing the matrix of pins 126 and 136. Outside pins 128
and 138, located at the bottom-side of chip package (in both packaging
cases) connect with the PCB, whereas topside of the package is connected
with the heat sink to dissipate heat from the die. Both types of packages
provide closer proximity of signal as on-chip. The fidelity of signal
occurred due to the conventional electrical off-chip interconnections 110
through multiplayer PCB 100. It is highly desirable having the
board-level electrical signal connection for high-speed off-chip
connection, which could be compatible with existing IC package such as
BGA, CSP etc., and also could be employed conventional PCB technologies.

[0007]To alleviate the problems such as cross talk, electromagnetic
interference etc. usually occur in the high speed electrical
interconnects, electrical signal lines in off-chip interconnects are
partially replaced by the optical interconnects using the optical fiber
or optical waveguide as the media. This is because the optical signal
eliminates EMI problem and also reduces the generation of loss for even
longer signal line interconnects. Many papers and patents applications
(both international and US) disclose concerning optical interconnects in
off-chip connection. One typical example is disclosed in Toshiyoshi et
al., IEEE/OSA Journal of Lightwave Technology, Vol. 17, No. 1, pp. 19-25
(1999). In this report, chip-to-chip interconnection based on wavelength
division multiplexing (WDM) technique is proposed. Free-space optical
interconnection technique between IC chips are employed to transfer and
receiving the optical signal using of micro-electro-mechanical system
(MEMS) device. The proposed concept is similar to conventional WDM
technique, frequently used in optical communication. This technique could
increase the capacity per channel. However, if this technique is used in
off-chip interconnections where chip-to-chip distance is few centimeters,
this technique will be make the whole interconnection bulky, and could
not be used in practical application where existing chip package and
conventional PCB technology are frequently used.

[0008]This WDM technique may have no problem for use in the board-to-board
interconnection where distances are few meters. However, in an
application where existing chip with package such as BGA and CSP are
used, the use of this free-space optic concept makes the interconnects
more bulky, and miniaturization is difficult to achieve. Furthermore,
free space optics concept is also not friendly to implement in the
electronics systems such as desktop computer and video-gaming system,
which are generally operated in dusty environment, and the deterioration
of optical signal transmission/receiver may happen due to poor signal in
long run system use. For the electronics system where miniaturization and
the cost are the issues, it would be highly desirable to design the
optical interconnects which could compatible existing chip package.

[0009]In conventional optical interconnects, where free-space optics
techniques and/or Z-direction of the chip is used for transmitting the
optical signal from transmitter to receiver, most of the time, cooling of
the electronics chips are not being considered in most of the inventions,
disclosed so far. With increasing of the on-chip speed, chip power
consumption is also increasing. For the case of the electronics chip,
dissipating large amount of heat, additional cooling system is necessary
and conventionally, z-direction is used for cooling purpose. Today's
optical interconnects where, chip's z-direction, is used for
transmitting/receiving the optical signal, in such optical interconnects
technique, cooling means can't be implemented and thereby, such optical
interconnects are impractical for high speed off-chip interconnects.

[0010]U.S. Pat. No. 6,434,308 B1 (inventor: Trezza) discloses a connector
system for the optical transceiver for interconnecting the chips through
an array of emitters and detectors. In this connector system, the fiber
bundles are used as a media to transmit and receive the optical signals
for off-chip communication. In the disclosed patents, chip with package
system aren't considered to make interconnects. The main drawbacks of
this connector system is that additional interface board including
packaging may necessary to make inerchip communication in chip with
package level communication. Furthermore, this way of communication using
of the fiber bundles prevents the system from miniaturization and not
suitable for the electronics system, especially for off-chip
communication. This connector system may suitable for the optical
interconnects, especially board-to-board interconnects.

[0011]U.S. Pat. No. 6,411,418 B1 (inventors: Deri et al.) discloses
architecture for multiprocessors interconnection using of WDM technique.
Here, independent channels on different optical wavelengths are
simultaneously broadcast to many nodes over a star coupler. No packaging
scheme is described compatible for the chip package. This scheme may
increase the bandwidth and latency and can't be applicable for the
off-chip interconnects for the application like electronics system where
chip with package level interconnects is concerned. Additional interface
board including packaging scheme is necessary to implement this
architecture.

[0012]As explained above, conventional electronics interconnect for
off-chip communication has the drawbacks that integration technology of
IC is not fully utilized, and also that exiting conventional electrical
interconnects have the limitation of maintaining available on-chip signal
speed. Today, the electrical interconnects among more than single chip
are done at the speed limit where the cross talk, electromagnetic
interference could be eliminated and this speed limit is below the speed
available in on-chip level. With increasing on-chip signal speed, it is
necessary to adopt interconnect technology which is compatible with
today's chip-package and also could be easily implemented in the
practical system.

[0013]Optical interconnects could eliminate the problems, that arises in
high speed electrical off-chip interconnects. However, optical
interconnects technology so far disclosed have also drawbacks that an
interconnect system are not compatible with the chip (with package) level
interconnects. For implementing the conventional optical interconnects
into the practical application, whole chip-package technology is required
to be developed or have different package technology compatible for the
disclosed optical interconnects. Furthermore, the conventional
interconnect technology is not friendly for manufacturing, which would be
costly and far from the practical application. In addition, today's
optical interconnects doesn't consider chip's cooling means. It is highly
desirable to have an optical interconnects technique which is compatible
to the today's chip-package and considers the chip cooling.

SUMMARY OF THE INVENTION

[0014]Accordingly, it is an object of the invention to provide an easily
stackable/mountable optical interconnect system by which on-chip level
signal speed can be maintained.

[0015]Another object of the present invention is to provide the
optical-electrical board, which is compatible with available chip package
and PCB technology.

[0016]Another object of the present invention is to provide the
fabrication techniques of the O-E (optical-electrical conversion) board,
which is compatible for the available chip package for the chip mounting.

[0017]Another object of the present invention is to provide the different
interconnects method for mounting the O-E board onto the chip-package.
This would help the users to both mechanically and electrically couple
and decouple the chip package from the O-E board with relative ease.

[0018]Another object of the present invention is to provide the
fabrication technique of the optical waveguide board stackable onto the
PCB board.

[0019]Another object of the present invention is to provide the
fabrication technique of the optical waveguide transferable onto the
conventional PCB.

[0020]Another object of this present invention is to provide the high
coupling efficiency waveguide board for increasing the tolerance in the
assemblies and also to reduce the dispersion of the optical signal.

[0021]Another object of this present invention is to provide the type of
optical devices and their fabrication techniques compatible for the O-E
board.

[0022]According to the invention, stackable optical interconnect system
for off-chip interconnects comprises:

[0023]a first chip with package; and a optical-electrical board for
(interfacing electronics chip package to PCB,) input/output (I/O) signals
from and to the electronic chip (hereafter mentioned as chip), optical
guiding board, and the PCB to connect with the neighboring chip and
circuit;

[0024]wherein the O-E board helps to connect the signal line and also
power and ground of the IC package to the PCB board.

[0025]The invention offers to connect the signal line of one chip to other
chip to communicate without sacrificing the signal speed available in
on-chip level. These inventions also use available chip package and the
PCB technology, so that additional modification of chip package is not
necessary to adapt this invention in practical application. The method
and apparatus described in this disclosure enables to make the optical
interconnects for off-chip interconnects in cost-effective manner and
suitable for practical electronics system applications.

[0026]Another advantage of this invention is that conventional PCB
technology with slight modification for optical waveguide implementation
could be used.

[0027]In accordance with the invention, the O-E board is to be properly
designed to covert optical-to-electrical and electrical-to-optical
signals for transmitting and receiving signals required for off-chip
communication. The O-E board for I/O signals could be fabricated on the
rigid substrate or on the flex-substrate using polymer materials. The
emitter and detectors required for converting electrical-to-optical and
optical-to-electrical signals are hybridly fabricated onto the O-E board.
The optical signals (from and to the O-E board) are based on the
free-space optics. In order to reduce the dispersion of the signals and
easiness in the assembly for cost-effective board fabrication,
pre-positioned micro-mirror, or micro grating are used onto the
waveguide, which can increase the tolerance in the assembly. Stacking of
the O-E board and the chip could be done using flip-chip bonding or based
on the pin connection. As the optical signal is taken out from the
bottom, the output electrical connections are power and ground which
could taken out through O-E board, and the foot-print could be the same
as the chip.

[0028]In accordance with the invention, the electrical contacts are
designed to efficient heat dissipation from chip-package to PCB, which
help to replace the complex cooler being used in today's chip (for
example processor) cooling. The electrical contacts are arranged in such
a way that the contacts for grounding is arranged in the peripheral
outline which at the same time acted as the tunnel for the heat
dissipation from the chip to PCB. Alternatively, the wider electrodes
targeting for the heat dissipation can be designed.

[0029]Other object of this invention is to minimize the skew in the signal
interconnection, occurred due to the signal delay, by transforming the
high-speed signal into the optical signal.

[0030]Other objects, features, and advantages of the present invention
will be apparent from the accompanying drawings and from the detailed
description that follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]The invention will be explained in more detail in conjunction with
the appended drawings wherein,

[0033]FIGS. 2A and 2B are top and cross-sectional views showings BGA based
chip package for high-speed die package. This is an explanatory diagram
showing chip package as mentioned in FIGS. 1A, 1B and other FIGS in this
invention;

[0034]FIGS. 3A and 3B are top and cross-sectional views showings CSP based
chip package for high-speed die package. This is an explanatory diagram
showing chip package as mentioned in FIGS. 1A, 1B and other FIGS in this
invention;

[0035]FIGS. 4A and 4B are simplified top and cross-sectional views taken
along B-B' section, illustrating the inter-chip connection employing the
optical interconnects in a first preferred embodiment according to the
invention;

[0036]FIG. 5 is a simplified cross-sectional view of the structure
including the chip-package, O-E board, and underlying PCB according to
the present invention;

[0037]FIG. 6 is a plan bottom view of O-E board for BGA package
constructed in accordance with the invention;

[0038]FIGS. 7A and 7B are a plan bottom view of O-E board for BGA package
constructed for the array of emitters (or detectors) fabricated on the
same wafer in accordance with the invention;

[0039]FIG. 8 is an enlarged cross-sectional view of an O-E board taken
along section line 5-5 of FIG. 6 illustrating an interconnect structure
for the package in FIG. 6. for the preferred embodiment in accordance
with the present invention;

[0042]FIGS. 11A, 11B, and 11C are the enlarged schematic cross-sectional
view equivalent to FIGS. 8, 9 and 10 of an alternate embodiment for
interconnecting the chip package and O-E board;

[0043]FIGS. 12A, 12B, and 12C are the enlarged schematic cross-sectional
view equivalent to FIGS. 11A, 11B and 11C of an alternate embodiment for
interconnecting the chip package and O-E board;

[0044]FIGS. 13A, 13B, and 13C are the enlarged schematic cross-sectional
view equivalent to FIGS. 12A, 12B and 12C of an alternate embodiment for
interconnecting the chip package and O-E board;

[0045]FIGS. 14A, and 14B are the enlarged schematic cross-sectional view
equivalent to FIG. 8 of an alternate embodiment for interconnecting the
chip package and O-E board;

[0046]FIGS. 15A, and 15B are the enlarged schematic cross-sectional view
equivalent to FIG. 8 of an alternate embodiment for interconnecting the
chip package and O-E board;

[0047]FIGS. 16A, and 16B are the enlarged schematic cross-sectional view
equivalent to FIG. 8 of an alternate embodiment for interconnecting the
chip package and O-E board;

[0048]FIGS. 17A and 17B are the enlarged top and schematic cross-sectional
views taken along A-A' direction in accordance with this invention;

[0049]FIG. 18 is the enlarged cross-sectional view equivalent to FIG. 17B
of an alternate embodiment according to this present invention;

[0050]FIG. 19 is the enlarged cross-sectional view of array of VCSEL in
the preferred embodiment according to this invention;

[0051]FIGS. 20A and 20B are the enlarged cross-sectional view of the
bottom emitting VCSELs in the preferred embodiment according to this
present invention;

[0052]FIGS. 21A, 21B and 21C are the enlarged cross-sectional view of the
bottom emitting VCSELs equivalent to FIGS. 17B, 18, 19, and 20B of
alternate embodiments according to this present invention;

[0053]FIGS. 22A, 22B and 22C are the enlarged cross-sectional view of the
top emitting VCSELs in the preferred embodiments according to this
present invention;

[0054]FIGS. 23A, 23B, 23C, and 23D are the enlarged cross-sectional view
of the edge emitting light source and the means making the beam as top
emitting equivalent the VCSELS of alternate embodiments according to this
present invention;

[0055]FIGS. 24A, 24B and 24C are the enlarged cross-sectional view of the
edge emitting light source with the monolithic modulator, and the means
equivalent to FIGS. 23B, 23C, and 23D of alternate embodiments according
to this present invention;

[0056]FIGS. 25A, 25B and 25C are the enlarged cross-sectional view of the
connection schemes of the VCSELS with the substrate/carrier of the O-E
board in the preferred embodiment according to this present invention;

[0057]FIGS. 26A, and 26B are the enlarged cross-sectional view of the
connection schemes of the VCSELS and drivers to the common carrier in the
preferred embodiment according to this present invention;

[0058]FIGS. 27A and 27B are the enlarged cross-sectional view of the top
incidence photodetector in the preferred embodiment according to this
present invention;

[0059]FIGS. 28A and 28B are the enlarged cross-sectional view of the
bottom incidence photodetector in the preferred embodiment according to
this present invention;

[0060]FIGS. 29A and 29B are the enlarged cross-sectional view of the
bottom incidence photodetectors in the preferred embodiment according to
this present invention;

[0061]FIG. 30 is a plan top view of waveguide board constructed in
accordance with the invention;

[0062]FIGS. 31A and 31B are the enlarged cross-sectional view of the
waveguide board taken across AA' and BB' directions, respectively, of
FIG. 30, in the preferred embodiments according to this present
invention;

[0063]FIGS. 32A, 32B, 32C, 32D, and 32E are the enlarged cross-sectional
view of the waveguide processes taken across BB' directions of FIG. 30,
in the preferred embodiment according to this present invention;

[0064]FIGS. 33A, 33B, 33C, 33D, and 33E are the enlarged cross-sectional
view of the waveguide processes, equivalent to FIG. 32 of an alternate
embodiment according to this present invention;

[0065]FIGS. 34A, 34B, 34C, 34D, and 34E are the enlarged cross-sectional
view of the waveguide processes, equivalent to FIG. 32 of an alternate
embodiment according to this present invention;

[0066]FIGS. 35A and 35B are the enlarged cross-sectional view of the
waveguide board, equivalent to FIG. 32E of alternate embodiments
according to this present invention;

[0067]FIGS. 36A and 36B are the enlarged cross-sectional view of the
waveguide board, equivalent to FIGS. 35A and 35B of alternate embodiments
according to this present invention;

[0068]FIGS. 37A, 37B, 37C, 37D, and 37E are the enlarged cross-sectional
view of the waveguide-board fabrication processes, taken across AA'
directions of FIG. 30, in the preferred embodiment according to this
present invention;

[0069]FIGS. 38A and 38B are a plan top view and the enlarged
cross-sectional views of waveguide, taken across AA' direction in FIG.
38A, constructed in accordance with the invention;

[0070]FIGS. 39A and 39B are a plan top view and the enlarged
cross-sectional views of waveguide, taken across BB' direction in FIG.
39A, constructed in accordance with the invention;

[0071]FIGS. 40A and 40B are a plan top view and the enlarged cross
sectional views of waveguide equivalent to FIG. 39B of alternate
embodiments, constructed in accordance with the invention;

[0072]FIGS. 41A, 41B, 41C, 41D, and 41E are the enlarged cross-sectional
view of the waveguide-board fabrication processes, taken across AA'
directions of FIG. 38A, in the preferred embodiment according to this
present invention;

[0073]FIGS. 42A and 42B are the enlarged cross-sectional view of the
master mold fabrication process in the preferred embodiment according to
this present invention;

[0074]FIGS. 43A, 43B, 43C, 43D, and 43E are the enlarged cross-sectional
view of the waveguide-board fabrication processes, equivalent to FIG. 40
of an alternate embodiment, constructed in accordance with the invention;

[0075]FIGS. 44A, 44B, 44C, 44D, and 44E are the enlarged cross-sectional
view of the master mold fabrication process, equivalent to FIG. 42 of an
alternate embodiment according to this present invention;

[0076]FIGS. 45A, 45B, and 45C, are a plan top view and the enlarged
cross-sectional views of waveguide, taken across and AA' and BB'
directions, in FIG. 45A, constructed in accordance with the invention;

[0077]FIGS. 46A and 46B are the enlarged cross-sectional views of
waveguide mounting techniques in the preferred embodiment, constructed in
accordance with the invention;

[0078]FIGS. 47A and 47B are the enlarged cross-sectional views of
waveguides, taken across AA' and BB' directions in FIG. 45A, constructed
in accordance with the invention;

[0079]FIGS. 48A and 48B are the enlarged cross-sectional views of
interconnects of the waveguide (as shown in FIG. 47) and the underlying
PCB, in the preferred embodiment, constructed in accordance with the
invention;

[0080]FIGS. 49A and 49B are the enlarged cross-sectional views of
waveguides, taken across AA' and BB' directions in FIG. 45, constructed
in accordance with the invention;

[0081]FIGS. 50A and 50B are the enlarged cross-sectional views of
waveguide mounting techniques for the waveguides as shown in FIG. 49B, in
the preferred embodiment, constructed in accordance with the invention;

[0082]FIGS. 51A and 51B are the enlarged cross-sectional views of
waveguides, taken across AA' and BB' directions in FIG. 45A, constructed
in accordance with the invention;

[0083]FIGS. 52A and 52B are the enlarged cross-sectional views of
waveguide mounting techniques for the waveguides as shown in FIG. 51B, in
the preferred embodiment, constructed in accordance with the invention;

[0084]FIGS. 53A and 53B are the enlarged cross-sectional views of
waveguide boards, mounted on the PCB in the preferred embodiment,
constructed in accordance with the invention;

[0085]FIGS. 54A, 54B, and 54C are the enlarged cross-sectional views of a
packaged chip, O-E board containing the array of optical components, and
underlying PCB board, illustrating an interconnect structure for the
package for the preferred embodiment in accordance with the present
invention;

[0086]FIGS. 55A and 55B are the enlarged cross-sectional views of an O-E
board containing the optical components and driver, and with underlying
PCB board, equivalent to FIG. 54 of an alternate embodiment interconnect
accordance with the present invention;

[0087]FIGS. 56A, 56B, and 56C are the enlarged cross-sectional views of a
CSP based chip-packaged, an O-E board containing the optical components,
and with underlying PCB board, equivalent to FIG. 54 of the alternate
embodiment interconnects accordance with the present invention;

[0088]FIGS. 57A and 57B are the enlarged cross-sectional views of a CSP
based chip-packaged, an O-E board containing the optical components, and
with underlying PCB board, equivalent to FIG. 55 of the alternate
embodiment interconnects accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0089]Four best modes for carrying out the present invention will be
described in turn with reference to the accompanying drawings. In the
following description, the same reference numerals denote components
having substantially the same functions and arrangements, and duplicate
explanation will be made only where necessary.

[0090]An important point of optical interconnects system for high speed
off-chip connection according to the first embodiment is the idea that
essential part, an optical-electrical (hereafter mentioned as "O-E")
board is required and it is to be compatible and easily stackable with
the available chip package and also PCB. To make the cost-effective, the
board should be friendly for the manufacturing as the electronics
components.

[0091]In off-chip interconnection, the signal between the chips may be
conveyed electrically through the wire or optically through the optical
media. Especially, the idea is to transfer the high-speed signal from one
chip to another after conversion into optical from electrical and
vice-versa for the receiving signal. The low speed signal connection and
the rest of the others connection such as ground and power line
connections are done through the electrical wire. When the signals are
conveyed by light (i.e. optically), the optoelectronics devices provide
the conversions between the light and electrical representations of the
signals.

[0092]FIG. 4A is the schematics showing the top view of optical
interconnects system for off-chip interconnects in accordance with the
invention. FIG. 4B is a cross-sectional view taken along a direction B-B
in FIG. 4A. The chip 120A (or 130A) communicates with chip 120B (or 130B)
by optically.

[0093]As shown in FIGS. 4A and 4B, the optical-electrical board 140 has a
structure in which chip 120A (or 130A) is stacked or mounted on a PCB
101. The chip 120A (or 130A) can communicate with chip 120B (or 130B)
through the optical connects of 112. The high speed electrical signals of
the chip 120A (or 130A ref. FIG. 3) and 120B (or 130B) are converted into
optical signals by the O-E boards 140A and 140B, respectively, located in
each side of the chip. The high-speed optical signals 114 and 116 can
transmit to and receive from other chip through array of optical
waveguide 112.

[0094]First, the arrangement of this optical-electrical printed board 140
(or 150) will be explained with reference to FIGS. 4A and 4B, in the
order of different O-E board structures based on the chip packages,
fabrication, and connecting means for electrically connecting the chips.
For the sake of simplicity, one side of the chip (for example 140A) is
only considered. Similar interconnects could be expected for the case of
O-E board of counterpart chip.

[0095]FIG. 5 is the simplified cross-sectional view of the structure
including the chip-package 120A, O-E board 140A, and underlying PCB 101A
according to the present invention. For simplicity in the explanation,
one side of the chip is considered, similar interconnects could be
assumed for counterpart chip. Chip package using of BGA or fine BGA is
considered.

[0096]FIG. 6 is a plan view, showing from the optical part mounting side
(bottom), the O-E board 140 according to the second embodiment. The O-E
board 140 for interconnects is included a singulated chip (with package)
120 and a singulated portion of the circuit 152. The O-E board 140 and
the circuit 152 have peripheral outline substantially similar to that of
the package 120. The circuit 152 includes a substrate 150, which
comprises with insulating, flexible material or rigid material. The
flexible material could be any kinds of polymer material, which includes
polyimide, polyester, epoxy, urethane, polystyrene, silicon or
polycarbonate. The substrate 152 also includes the rigid substrate.
Suitable materials for the rigid substrate cover ceramic materials
including aluminum nitride, aluminum oxide, and boron nitride. The
material having high thermal conductivity and high dielectric constant
also covers this substrate material. The thickness for the substrate 152
can be 20 to 500 um.

[0097]The circuit 152 of the O-E printed board also includes an array of
external contacts 154 and 156 formed on a first side of the substrate
150. The external contacts 154 are for the electrical contacts especially
for the power and ground connects to the PCB 101, and whereas the
external contacts 156 are for the contacts for the optical components
connects. In the illustrative embodiment (FIG. 8) the external contacts
154 and 156 are metal balls on the metal plat 158 and 160. Each external
contact 154 and 156 can be hemispherical, convex or dome shaped with the
diameter "D" and height "H". The diameter and height can be vary from 25
μm to 1 mm. Especially for the contacts 156 which are in contact with
the optical components, "D" and "H" are to be selected in a way that the
inductance and capacitance induced due to the contact don't have an
affect on the converted O-E signals. The pitch and the density of the
contacts 154 and 156 can be selected as required. The external contacts
154 and 156 can be arranged in dense array in the form of BGA or fine
BGA. For simplicity in FIG. 6, the external contacts 154 and 156 are
illustrated in an array of two rows. However, some dense arrays can cover
the entire face of the chip package 120 and hundreds (and thousands) of
external contacts 154 and 156.

[0098]The external contacts 154 and 156 can comprise a solder alloy which
includes 80Au: 20Ge, 80Au: 20Sn, 10Au: 90Sn, 94Au: 6Si, 25Sn: 75Pb, 30Sn:
70Pb, 40Sn: 60Pb, 50Sn: 50Pb, 63Sn: 37Pb. Especially, the contacts 156,
which connect with optical devices, can have the alloy with higher
melting point. The external contacts 154 and also 156 can comprise the
pre-fabricated solder balls bonded to solder wettable land pads 158 and
160 (ref. FIG. 8). Alternately, the contacts 154 and 156 can be formed
using electro-plating deposition or electro less deposition process to
deposit pads and balls of desired materials. Again, alternately, the
contacts 154 and 156 can comprise a conductive polymer material such as
metal filled epoxy bumps formed by a stencil process.

[0099]The number of discrete optical components, for examples emitters 162
and photodetectors 164 are bonded on the contacts 156, to convert the
high speed electrical signals into optical signals and vice versa. Solder
alloy as mentioned before can be used for bonding the optical components
onto the substrate 150. Picked and placed technique frequently used IC
manufacturing can be used. The position of the optical components can be
determined by alignment marker (not shown) formed on a substrate 150. The
contacts 156 are designed in a way that single contacts 166 and 168 of
156 can be used for common cathode connection for the emitters 162 and
for the photodetectors 164, respectively.

[0100]Alternately, the array of emitters 170 and photodetecors 172 having
anode-cathode pair, fabricated on single wafer can also be used in the
O-E printed board 140, as shown in FIG. 7A. Alternately, the array of
emitters 174 and array of photodetectors 176 having a common cathode 178
and 180 for both emitters and photodetectors respectively can also be
used in the O-E board 140.

[0101]As shown in FIGS. 6, 7A, and 7B, the circuit 152 of the O-E printed
board 140 also includes a pattern of conductors 190 formed on second side
of the substrate 150 of the O-E board 140 for electrical communication of
the external contacts 154 and 156. The second side is connected with the
chip side. The conductors 190 can be formed onto the substrate prior to
the formation of the contacts 154 and 156 to connect. The conductor's
patterns 190 can be formed as follows: First, metal layer is deposited on
the substrate 150 using of sputtering, or evaporation. The patterning and
etching to form the conductor patterns 190 follow this. Highly conductive
metal such as gold, plated gold, copper, plated copper, Ni or Ni-based
alloy is preferable for the conductors 190. The thickness of the metal
varies from 1 um to 50 um. Instead of using the deposited metal, the
electro-plating deposited metal can be used for forming the conductor's
patterns 190. The length of the conductor patterns 190 on the substrate
150 varies from few um to few mm. For longer pattern length, the
conductor pattern 190 could be micro-strip line or coplanar line to be
designed based on the signal speed.

[0102]FIG. 8 is an enlarged cross-sectional view of the O-E printed board
taken across 5-5 section of FIG. 6 in the preferred embodiment according
to the present invention, wherein like parts are indicated by like
reference numerals as used in FIGS. 6 and 7, so that repeated explanation
is omitted here. In FIG. 8, the electrical interconnect between O-E
printed board 140 and the chip package 120 comprise the conductors
pattern 190 which connect with the solder bumps 192 on the chip package
contacts 194 through the conductive polymer layer 196 in between O-E
board and the chip package. This technique offers high tolerance, which
makes easiness in the mounting the chip onto the O-E board.

[0103]Suitable material for conductive materials includes Z-axis
anisotropic adhesive and Z-axis epoxies. The Z-axis conductive
anisotropic adhesive provides electrical conductivities along Z-axis,
while providing isolation along x-axis. Using of conductive polymer layer
196, makes electrical connection is made between the solder bumps 192 on
chip with the conductor pattern 190. Based on the signal speed the
thickness of the conductive polymer layer 196 is to be selected, and it
is from 2 μm to 500 μm. Insulation layer 198 is used to
electrically isolate the chip contacts with the other contacts. The
solder bumps 192 on the chip contacts 194 comprise with the solder alloy
as described above, or can be electro-plating deposited using the process
as described in the U.S. patent application Ser. No. 08/905,870,
mentioned herewith for reference only. The melting point is lower than
the solder alloy used for bonding the optical components on the O-E board
140. The material type can be selected as required.

[0104]FIG. 9 is an enlarged cross-sectional view of the O-E printed board
taken across 5-5 section of FIG. 6 in the preferred embodiment according
to the present invention, wherein like parts are indicated by like
reference numerals as used in FIGS. 6, 7 and 8, so that repeated
explanation is omitted here. Here, additional polymide resin layer 200 is
used on the top of the optical components. This polymide layer protects
the optical components from damage. The refractive index of the polymide
layer is >1.55 and it can be selected suited for the wavelength of the
optical signal transmitted through the layer. Suitable polymide materials
include the epoxy resin, fluorinated polymide-based resin or fluorinated
epoxy based resin. The polymide can be formed by spin coating, which is
followed by curing at temperature below 50 C to 350 C, or by ultra violet
curing.

[0105]FIG. 10 is an enlarged sectional view of the O-E printed board
equivalent to FIG. 9 in the preferred embodiment according to the present
invention, wherein like parts are indicated by like reference numerals as
used in FIGS. 8 and 9, so that repeated explanation is omitted here.
Here, the integrated microlens is formed onto the polymide layer 200.
This is either to focus or to collimate the beam 204 so that high
efficiency waveguide coupling is possible without using of any additional
optics in between. The tolerance in the assembly is also achieved using
this. The microlens can also have a compound lens structure to achieve a
better-optimized beam profile. The microlens can be made using the
standard microlens fabrication techniques such as resist reflow
(refractive lens) and dry etching (diffractive lens). Reflow resist such
as AZ4620 can be used as the lens material. Alternately, the molded
plastic lens 202 with required focal length can also be used onto the top
of the polymide layer 200. Suitable material for the lens can be the same
material as polymide layer 200, or different polymer materials such as
polymethyl methacrylate (PMMA), Styrene, butadiene, butadiene and styrene
based polymer (e.g. acrylonitrile-butadiene-styrene (ABS)) resins,
polycarbonate, and acryl. To increase the mechanical strength, butadiene
based rubber-reinforced resin, as noted in U.S. Pat. No. 6,448,342
(Inventors: Takahashi et al.). The refractive index of polymer material
used here as molded plastic lens or reflowed resist have the refractive
index >1.55, and can be selected closer to the underlying layer 200.
Same material can be used for both layer 200 and the lens material, and
the process can be done one time.

[0106]FIGS. 11A, 11B and 11C are the enlarged sectional view of the O-E
printed boards equivalent to FIGS. 8, 9, and 10 in the preferred
embodiment according to the present invention, wherein like parts are
indicated by like reference numerals as used in FIGS. 8 9, and 10, so
that repeated explanation is omitted here. The solder bumps 206 on O-E
printed circuit conductors 190, and 192 on packaged-chip contact 194 are
used to electrical connects. Suitable materials for solder materials are
previously mentioned, and the melting points are lower than those used in
bonding the optical components on the O-E printed circuit. Conductive
polymer bumps can also be used in this case, and suitable material
includes anisotropic adhesive or isotropic adhesive as mentioned
previously. Polymer bumps can be formed by dot shooting through nozzle,
and can be formed in a half-cured and fully cured after making the making
the contacts. Full curing can be done either by UV irradiation or
temperature treatment. Electrically insulating adhesive layer 208 is used
in between the packaged-chip and the O-E board 140. The material for
insulating layer 208 can be chosen to act not only for electrically
insulating, but also for the physically attache the O-E board 140 onto
the chip-package 120. Curable either by UV irradiation or temperature
treatment, adhesive can be chosen for this layer 208 formation. Suitable
materials for insulating adhesive layer include, but not limited to,
cyanoacrylate adhesives (commercialized by Loctite Corp, Rocky Hill,
N.J.) and also silicon elastomer such as ZYMET (manufactured by ZYMET,
East hanover, NJ) can be used for this purpose.

[0107]FIGS. 12A, 12B and 12C are the enlarged sectional view of the O-E
printed boards equivalent to FIGS. 11A, 11B, and 11C in the preferred
embodiment according to the present invention, wherein like parts are
indicated by like reference numerals as used in FIGS. 11A, 11B, and 11C,
so that repeated explanation is omitted here. In this preferred
embodiment, the O-E board 140 is connected with the chip package 120 with
help of the solder bumps or conductive polymer bumps formed on both
contacts. Suitable type of the bumps includes the types previously
described. In this embodiment, a compliant layer 210 is used in between
the O-E board 140 and chip package 120. This layer 210 matches the
differences in thermal expansion of O-E board and chip package, if any.
The difference in thermal expansion may cause high stress during change
of temperature and may cause fatigue and crack in the optical components
and also solder bumps, electrical conductors. The coefficient of the
thermal expansion of layer 210 is selected in between the CTE of
substrate 150 and CTE of O-E board and chip package to compensate the
thermal expansion during temperature changes. The compliant layer 210 can
be formed by dispensing method, which includes spin-on, stencil, and
capillary action to fill the gap between the O-E board and the chip
package. Alternatively, the layer 210 can come with the O-E board, and
could be formed by film deposition or spin coating, and patterning, and
subsequent etching to open for the bumps. Suitable material for layer 210
includes all kinds of polymer material, which has the CTE value in
between the O-E substrate and chip package. One suitable material is
HYSOL Brand FP4520 (commercialized by Dexter Electronics Materials).
Compliant layer 210 can be single layer or multiple layers of different
material to compensate the CTE of chip-package and O-E board can also be
used.

[0108]FIGS. 13A, 13B and 13C are the enlarged sectional view of the O-E
printed boards equivalent to FIGS. 12A, 12B, and 12C in the preferred
embodiment according to the present invention, wherein like parts are
indicated by like reference numerals as used in FIGS. 12A, 12B, and 12C,
so that repeated explanation is omitted here. In the preferred
embodiment, single bumps 212 are used on the chip package contact 194.
Suitable bump material includes alloy type solder, conductive polymer, as
described previously. The bumps can be formed using the dispensing
technique or the dot-shot, as explained earlier. The height of the bumps
is selected as required. The compliant layer 206 or 208 in between O-E
board and chip package could be adhesive as explained previously.

[0109]FIGS. 14A and 14B are the enlarged sectional view of the O-E printed
board and chip package in the preferred embodiment according to the
present invention, wherein like parts are indicated by like reference
numerals as used in FIGS. 11A, 12A, and 13A, so that repeated explanation
is omitted here. Referring to FIGS. 14 A and 14B, adhesive layer 214 is
used in between the O-E board 140 and chip package 120. The preformed
hole 216 and 218A through the adhesive layer 214 and O-E substrate 150,
respectively, helps to make interconnects between the O-E board and chip
package. A bonding tool 220 is used through the holes to make the bonded
connection 222 between O-E printed circuit 190B and the chip package
contacts 194. The layer 214 can be the preformed layer placed onto the
chip package at the edge of the contacts. Alternatively, the layer 214
can be the separate from O-E board, and chip package, and it can be the
form of the thin flexible layer, and is used while bonding. The adhesive
layer 214 is electrically insulating adhesive. Suitable material for this
adhesive layer covers all polymer-based adhesives having high electrical
insulation. The bonded tool can be thermocompression, or thermosonic
tool, which can generate heat to make bonding. The metal for the printed
circuit 190B is to be high thermal conductivity and those are gold,
copper, pladium or nickel.

[0110]FIGS. 15A and 15B are the enlarged sectional view of the O-E printed
board and chip package in the preferred embodiment according to the
present invention, wherein like parts are indicated by like reference
numerals as used in FIGS. 11B, 12B, 13B, and 14, so that repeated
explanation is omitted here. In this preferred embodiment, the O-E board
comprises the printed circuit on the substrate 150, bonded optical
component 162, and the encapsulation of the optical components. The
encapsulation includes a preformed hole 218B through which bonding tool
helps to make the connection 220 between O-E circuit 190B and chip
package contacts 194. Refer to FIG. 15B, following the formation of the
connection 220, the hole can be filled by adhesive. For filling, standard
dispensing technique as described earlier can be used. Suitable adhesive
material includes the any electrically insulating adhesive or the same
adhesive of encapsulation.

[0111]FIGS. 16A and 16B are the enlarged sectional view of the O-E printed
board and chip package in the preferred embodiment according to the
present invention, wherein like parts are indicated by like reference
numerals as used in FIGS. 15 and 13C so that repeated explanation is
omitted here. In the preferred embodiment, the O-E board comprises the
printed circuit on substrate 150, bonded optical components 162,
encapsulation and the microlens. The microlens is formed as mentioned
previously. The material can be the same as the encapsulation material or
different. Alternatively, molded plastic lens for either focusing or
collimating purpose can also be used. The material and formation are
already explained previously.

[0112]The O-E board and its interconnects with the chip package described
above can be directly incorporated in envisioned off-chip module
integration applications that require the vertical interconnection. The
printed circuit of O-E board is employed to covert/receive high speed
optical signal using of the optical components bonded on the O-E board,
and also interconnects upper chip to a underlying PCB board in vertical
dimension, in parallel. The advantages of this interconnect technique is
that, standard cooling technique for heat dissipation from chip can be
used at top (e.g. for processor) and they can be employed without any
changes. As mentioned previously, only high-speed signals are converted
into optically for off-chip communicating. Others such as ground and
power connections can be without changes. This provides the advantages of
quick implementation in the practical electronics system where high-speed
off-chip interconnects are required.

[0113]Optoelectronics component (emitters for light conversion and
detectors for electrical signal conversion) compatible for the O-E board
140 described above provide the in/out light in vertical direction. For
light source, vertical cavity surface emitting laser (VCSEL) or edge
emitting laser can be used. Suitable wavelengths of light include 650 nm,
850 nm, 980 nm, 1310 nm or 1550 nm. FIGS. 17 A and 17B are the enlarged
top and cross-sectional view of the array of VCSEL 174 (Ref. FIG. 7B).
For simplicity in drawing, array of two VCSELs 162B and one cathode 224
are only shown. VCSEL can be fabricated using of GaAs substrate 222 for
the wavelengths 650 nm, 850 nm and 980 nm VCSEL, and InP for 1310 and
1550 nm. Other suitable substrate includes semi-insulating GaAs,
semi-insulating InP, Si, SiC, and Sapphire. The light 204 can be taken
out from bottom of the wafer. For simplicity in bonding onto the O-E
substrate 150, the contacts for anode 162B and cathode 224 can be taken
from the same side. If array of VCSEL are used in the O-E substrate 150,
common (single) cathode configuration for entire array, as shown in FIG.
7B can be used while fabricating VCSEL on a single wafer. Otherwise, in
the case of the discrete VCSEL case, separate cathode (Ref. FIG. 6) is
necessary, which can be connected together on the O-E substrate 150.
Pixel sizes of VCSEL for the single mode operation are from 5 to 10
μm, and shape can be square or rectangular. For easiness in the
bonding, the electro-plated metal can be deposited on each pixel, and the
electrode size (diameter) may vary from 10 to 50 μm. The height can be
selected as required for the bonding. Suitable metal for electrode
formation includes gold, copper, nickel. This metal deposition is after
ohmic contact formation for anode and cathode. As the VCSEL (as shown in
FIG. 17A), is mounted on O-E substrate 150 facing-up the substrate 222
(not shown), efficient heat dissipation is possible if the diameter of
the electrode (anode) is 20 to 50 μm. Suitable thicknesses of
electrodes (anode and cathode) for easiness in bonding are 10 to 50
μm. The detail fabrication process is cited in literature, IEEE/OSA
Journal of Lightwave Technology, vol. 76, no. 5, pp. 870-875, 1998. can
be found. The emitters can also be bonded using the flip-chip bonding
technique, which enables both to electrical, interconnects and to
laterally self-align the components as required for precision optical
alignment. The flip-chip bonding technique uses the solder bumps on the
electrical contact pads and reflowing the solder to form the
interconnections.

[0114]Referring to FIG. 18, additional polymide layer 226 can be used
electrically isolate the anode, required in the bonding. Suitable
polymide material includes all kinds of electrically isolated polymers.
This layer may be formed by spin coating, dispensing or standard
deposition technique, which includes the sputtering, CVD, evaporation
polymerization, or other vapor phase deposition methods. The
photolithography based patterning and subsequent etching (chemical or dry
etching) makes the opening on the anode for the contacts. Alternatively,
chemical mechanical polishing (CMP) may be also used to polish unwanted
polymide thickness to open the anode and cathode electrode opening.

[0115]FIG. 19 is an enlarged cross-sectional view of the VCSEL array,
equivalent to FIG. 17B in the preferred embodiment according to the
present invention, wherein like parts are indicated by like reference
numerals as used in FIGS. 17B and 18, so that repeated explanation is
omitted here. In this preferred embodiment, after the wafer polished to
100 um, the portion of the VCSEL substrate is wet etched to make the
trench 228 under the pixel. This enables to increase the optical power 30
to 40% of the beam 204C for the case of 980 nm VCSEL, fabricated onto the
GaAs. Alternatively, the VCSEL array itself can also be transferred to
the suitable substrate 230 by vapor phase epitaxial lift-off (EPL)
technique, described by Chang et al., in Fall Materials Research
symposium, paper H10.1 of session H10, 1997. FIG. 20A shows the VCSEL ELO
process for transferring to alternate substrate 230. This enables to
convert bottom-emitting VCSEI to top-emitting VCSEL, and enhance further
optical output 204D. Suitable contacts 156B can be made backside of the
substrate 230 to make easiness in the bonding on the O-E substrate 150.
Suitable substrate for ELO process includes Si, glass, and polymer. As
the VCSEL device itself is very thin varying from 1 um to 6 um, top
surface of the VCSEL should be high adherence to the transferred
substrate. Increasing adhesion can be possible using of the thin layer of
metal layer on the VCSEL, and metal includes Tungstant and Chromium for
enhancement of the adhesion. Noted here that thick n+ layer in the case
of n-substrate (or p+ layer in the case of p-type substrate) is desirable
prior to epitaxial growth of the VCSEL structure for the case VCSEL,
which undergoes through the ELO process. This enables to increase the
yield of the ELO process. After transferring the VCSEL to the alternate
substrate friendly for manufacturing, the exposed VCSELs 162B can be
encapsulated by transparent adhesive layer 200B, as is shown in FIG. 20B.
Spin coating, followed by proper curing by UV irradiation or temperature
treatment, can form the adhesive or polymer layer 200B. Alternatively,
the layer 200B can be also formed by standard deposition techniques such
as sputtering, CVD, evaporation polymerization, or vapor-phase
deposition. The CMP technique is also used for planarization (not shown)
of the surface of the layer 200B. In this case, a thin protective layer
of metal is preferably coated onto the VCSEL prior to the formation of
the encapsulation layer 200B.

[0116]FIGS. 21A, 21B, and 21C are the enlarged cross-sectional view of the
VCSEL arrays, used to FIG. 17B, in the preferred embodiment according to
the present invention, wherein like parts are indicated by like reference
numerals as used in FIGS. 17B, 18, 19, and 20B, so that repeated
explanation is omitted here. Integrated microlens 232 (or 234) are formed
on to the back surface of the substrate 222 to correct the optical beam
profile so that laser beam propagating towards the back surface is
focused with a low divergence angle (collimated beam) for coupling into
the waveguide in the PCB. Referring to FIG. 21C, the microlens(es) 236
can be formed using the same encapsulation layer 200B using the standard
microlens process. This microlens enables to increase the tolerance in
the bonding Also this enables to reduce the driving current as required,
because the optical power is increased as compared with that of the VCSEL
without the microlens. The microlens may be a refractive lens, which can
be prepared, for example, a photoresist reflow process, and/or a
defractive lens, which can be prepared, for example, by dry etching. The
optical axis of the microlens (es) preferably passes through the
light-deflecting surface. To make a collimated output beam, the focal
length of the microlens should be designed to be around twice of the
substrate thickness, which can be quite easily achieved using the
standard microlens fabrication techniques such as reflow of the resist
(refractive lens) and dry etching (defractive lens). Suitable materials
for the microlens (es) include adhesive or epoxy, or polymer materials
having the refractive indices over 1.56.

[0117]FIGS. 22A, 22B, and 22C are the enlarged cross-sectional view of the
VCSEL arrays, used in FIG. 17B, in the preferred embodiment according to
the present invention, wherein like parts are indicated by like reference
numerals as used in FIGS. 17B, 18, 19, and 21, so that repeated
explanation is omitted here. In the preferred embodiment, array of top
emitting VCSEL 162C to be used in O-E board 140, are fabricated from GaAs
or InP, 222. The advantage of top emitting VCSEL as compared with that of
bottom emitting VCSEI is that the absorption of the light due to the
substrate is not exist. This enables to have high optical power of the
beam 204F at the fixed driving current. In order to avoid complexity in
bonding, the anode electrode 238 can be taken out from bottom of the
substrate through via hole, which can be made by wet or dry etching of
the substrate 222. Insulation layer 240, such as SiO2 or SiNx is
deposited prior to filling the hole with metal, enabling to isolate the
bottom contacts 242 of the anode electrode from the cathode (which is
back surface of the substrate). Referring to FIGS. 22B and 22C, the
encapsulation layer 200B using of the adhesive is formed on the top of
the VCSEL. This enables VCSEL protecting from damage during the assembly
and thereafter in long run operation. The micro-lens of 244 is formed
using of the same adhesive layer 200B or separate layer for microlens.
The formation of the encapsulation layer and microlens are described
earlier, so that the repeated explanation is omitted here.

[0118]FIGS. 23A, and 23B are the enlarged top and cross-sectional view of
vertical light emission device using of the edge-emitter, taken along
C--C' direction of FIG. 23A, in the preferred embodiment according to the
present invention, wherein like parts are indicated by like reference
numerals as used in FIGS. 22A and 22B, so that repeated explanation is
omitted here. The requirement of the high speed and high capacity optical
transmission system pushes the development of high-speed edge-emitter
technology, and now this technology is well matured that high speed edge
emitters having the bandwidth of 10 GHz and above are relatively
inexpensive. As one of the main objective of this present invention is to
make the cost-effective optical interconnects for inter-chip connection,
low-cost edge-emitter is also thought as the preferred embodiment to use
in the O-E board 140 as described earlier. Referring to FIG. 5, in the
present invention, the optical signal transmitting and receiving are
performed in vertical direction, and thereby, the emitter need to be
bonded in a way to provide the surface normal emission. Here vertical
emission is done using of the edge-emitter in conjunction with a mirror
to redirect the optical beam so that optical beam passes through the
underlying the optical media. The vertical emission device 246 as shown
in FIGS. 23A and 23B, illustrates a platform 246 with an edge emitter
246. The platform 246 comprises with two section; mounting section 246A
and beam reflecting section 246B. The reflecting section 246B has an
inclination surface 246B' having an angle of theta to reflect the beam
204 in vertical direction. The angle of inclination theta of the
reflecting surface 246B' is totally internally reflected at the reflected
surface 246B'. The minimum angle theta can be calculated from the
refractive index of the material forming the surface 246B' using the
Snell's Law. In the case where the reflecting surface 246B' acts as the
mirror, the angle of inclination should be 45 degree. In this case, the
surface is highly reflective. However, in the case where the reflecting
surface is not totally reflecting (i.e. no reflecting coating), optimized
theta design for total reflection is necessary. Suitable carriers for the
platform 246 include Si, GaAs, InP, SiC, polymer, glass, and ceramics
such as AlN, Al2O3. The surface 246B' should be highly reflective, and it
can be formed by highly reflecting metal coating or deposition technique.
Suitable reflecting metal includes aluminum, gold, tungsten, and
chromium. During bonding, the edge emitter 248 is positioned and aligned
with the help of the preformed alignment markers on the platform. In this
technique, the sub-micrometer range alignment can be possible.
Additionally, or alternatively pre-formed pedestals on the platform 246
can be used for positioning and aligning. In simplicity of drawing,
single device is shown. However, array of the edge-emitters, either
discrete or monolithically fabricated on a single wafer, can also be used
as illustrated in FIGS. 23A and 23B. The electrical connection 250 as
required can be made onto the platform 246, and/or taken out to the back
surface through VIA hole or through wrapping (not shown) the metal sheet
from top to bottom. For high-speed connection, proper transmission line
design may necessary for avoiding the deterioration of the electrical
signal before lunching to the edge emitter 248.

[0119]Referring to FIGS. 23C and 23D, further the device 162 comprises the
encapsulation layer 200B following bonding the edge-emitter (array) 248.
The type of material and its formation are already described earlier, so
that repeated explanation is omitted here. Following encapsulation,
planarization can be done using CMP. As referred to FIG. 23D, further the
device 246 comprise the microlens (es) 252 on the top of the
encapsulation layer 202B. The type of materials for microlens (es) 252
and microlens (es) formation are already described previously, so that
repeated explanation is omitted here.

[0120]FIGS. 24A, 24B, and 24C are the enlarged cross-sectional views of
vertical light emission device using of the edge-emitter integrated
modulator, equivalent to FIG. 23A in the preferred embodiment according
to the present invention, wherein like parts are indicated by like
reference numerals as used in FIGS. 23B, 23C, and 23D, so that repeated
explanation is omitted here. The hybridly integrated vertical emission
type device 162D, as shown in FIGS. 24A, 24B, and 24C, comprise the
modulator integrated laser diode 254, which has the laser diode 256 and
electro-absorption modulator, monolithically integrated on the signal
wafer, and platform 246 to reflect the beam 204J in upward direction.
Suitable substrate 222 include for this device include III-V based
semiconductor such as GaAs, InP, SiC, Sapphire. The electrical connection
for both laser diode and modulator can be made on the front side of the
platform 246, which can be taken out making and filling the VIA hole
through the platform carrier 246. As the high-speed signal requires feed
to the modulator section, microwave design for designing the transmission
line is required. Suitable matching circuit may requires to improve the
microwave performance of the electrical interconnects considering the
parasitic affect due to the contacts 250. Suitable matching circuit as
required can be designed on the platform carrier 246. Referring to FIG.
24B, the hybridly integrated vertical emission device 162D is
encapsulated by adhesive layer 200B. The type of the material and
technique of encapsulation formation is already explained previously, so
that repeated explanation is omitted here. Referring to FIG. 24c,
microlens(es) 260 is formed on the encapsulation layer 200B using the
material and technique, as described previously. Array of device (not
shown) here can also be made as illustrated in FIGS. 24A, 24B, and 24C.

[0121]In earlier descriptions, especially from FIGS. 17 to 24, the
edge-emitters, and surface emitters are directly bonded on to the O-E
board, understanding that either the required driving functionality is
incorporated into the chip, which is connected to the O-E board. This
functionality may include the electrical signal outputs in current
(direct modulation laser-diode) or voltage (external modulation using of
the modulator) form, which are essential to drive the edge emitter or
VCSEL or modulator. If the optical sources, means for converting the
electrical signal into optical signal, have not receive essential
electrical signal to generate enough optical power, the electrical driver
is necessary to boost the electrical signal prior to launching to the
optical sources. In that case, optical sources (edge-emitters, VCSEL or
modulator integrated laser diode) in array or discrete form, described in
FIGS. 17 to 24, and electrical driver chip are to be mounted onto the O-E
board substrate 150. FIGS. 25A, 25B, and 25C are the enlarged
cross-sectional views of VCSELs and driver chip bonding in the preferred
embodiment according to the present invention, wherein like parts are
indicated by like reference numerals as used in FIGS. 17 to 24, so that
repeated explanation is omitted here. The VCSEL 162C or 162B (both types;
bottom emitting and top-emitting type) chip(s) can be bonded on the
driver chip(s) 262 using the solder bumps to connect driver chip contacts
264 and VCSEL contacts 242.

[0122]The contacts 266 of the driver in back side of the substrate is made
through whole electrode, and connects with the O-E substrate. The through
hole electrode is formed by following fabrication technique, consisting
of (a) polishing the substrate to 100 to 120 um, (b) masking for
through-hole, (c) through hole formation using the dry etching technique
such as ECR-RIBE, RIE using appropriate reactant gas for example SiCl4
for GaAs substrate, (d) insulating layer formation, (e) patterning (back
side of the substrate) and subsequent metallization, for connecting the
bottom contacts 264. The driver chip with through hole electrode, and top
emitting VCSEL can be bonded with the substrate face down. Using of this
bonding enables efficient heat dissipation from the driver and VCSEL for
the case of the driver chip 262 and the top emitting type VCSEL 162C, the
substrate of which are faced down. For the case of bottom emitting VCSEL
162B, the substrate of which is face up, larger diameter of metal
electrode of the anode makes efficient heat dissipation. For this,
diameter is 10 μm to 50 μm. High conductive metal such as gold,
copper, nickel preferably used for the electrode formation, as described
previously. The type of solder material and bonding process are the same
as described previously. Flip-chip bonding technique can be used for
bonding and for self-alignment. Alignment marker can be used on to the
driver chip for pre-align the electrical contact pads. Using alignment
marker and also flip-chip bonding enables the bonding as low as pad
diameter of 5 μm with sub-micron range accuracy in x-y direction.
Noted here that, for simplicity in the drawing, the single driver and
VCSEL chips are shown. However, similar way of bonding can be performed
for the array of the driver on single wafer and array of the VCSELs on a
single wafer, monolithically fabricated together. Both driver chip and
VCSEL can be fabricated independently and bonded hybridly, as mentioned
previously, Suitable substrate and technology for driver chip fabrication
include Si substrate using the standard Si CMOS or Si:Ge technology, or
III-V semiconductors substrate such as GaAs, InP, GaN using standard
III-V technology.

[0123]Referring to FIGS. 26A and 26B, the driver 162C (or 162B)) can be
also bonded on to the common carrier 268. Suitable carrier substrate
includes Si, III-V semiconductor substrate, SiC, ceramics such as AlN,
Al2O3, sapphire, all polymer material having electrical insulation such
as polycarbonate, PMMA, ethyrin, flex polymer. The electrode 272 on the
common carrier 268, interconnects driver chip contacts 264A and VCSEL
anode contacts 242A. The contacts 270A and 270B of the carrier 268
connect with the O-E substrate, facing optical component and driver down.
The transmission line for high speed signal, and also matching circuit
(not shown) considering parasitic affect due to the solder bumps, through
hole electrode can be designed for avoiding electrical signal fidelity,
and those can be formed either on the common carrier 268, or can be
incorporated into the driver chip. Alternatively, VCSEL and driver can be
fabricated monolithically on a single wafer, for example on the GaAs or
InP substrate or GaAs on Si substrate.

[0124]From FIGS. 25 and 26, particular VCSEL and driver connections are
illustrated in the preferred embodiments according to the invention, for
simplicity. Similar technique can be used for the emitter case as
described in FIGS. 17 to 24. Also, referring to FIGS. 6 and 7, two
contacts for VCSEL is shown for the simplicity of the drawing. However,
the contacts cane more than two, as required for connecting the optical
components with the O-E substrate 150.

[0125]For inter chip communication, transmitting and receiving signal are
essential. In optoelectronics off-chip interconnects, O-E board 140 in
accordance with the present invention also comprises the
optical-electrical conversion capability. In this case, optical detectors
are incorporated on each O-E board at the location of the data or
signal-input ports. Each optical detector converts their respective light
signals to corresponding electrical representation, and provides their
representation to input circuit of the chip through corresponding
connection pads located in the chip package. The electrical represented
signal may or may not require amplifying. Amplifier may incorporate
inside the chip or discrete amplifier may require prior to input to the
chip. This is analogy to the transmitter with separate driver, as
described in FIGS. 25 and 26. Electrical signal in proximity to the
optical detector is essential, and it can be achieved using of the
suitable optical detectors (and receiver) having proper responsivity and
bandwidth, and proper interconnects on to the O-E substrate. All kinds of
the photodetector structure can be used in O-E board. Suitable structure
p-n, p-i-n, metal-semiconductor-metal.

[0126]From FIGS. 17 to 25, although the optical transmitting means (i.e.
optical sources) using of the surface emitting devices are illustrated, a
similar approach can be used for the receiver (i.e optical detectors).
For example, optical surface emitting type of devices (and also drivers)
can be replaced by surface coupled photodetectors (and amplifier or
transimpedance amplifier), including surface incidence and
bottom-incidence type photodetectors. The bonding techniques including
the enhancement of manufacturing tolerance by including the lens etc, as
described previously, can be all applied to the photodetector case, so
that repeated explanation herewith are omitted. Illustration hereafter
regarding photodetector includes type of the detectors and their
performance improvement in accordance with the present invention.

[0127]FIGS. 27A and 27B are enlarged top and cross-sectional views taken
along A-A' direction of FIG. 27A for the surface emitting type
photodetector in the preferred embodiment in accordance with the present
invention. The photodetector 164 comprises a semiconductor material with
a p-n junction formed in the material, with the p-type doped region
electrically coupled to one electrode 274A, and n-type doped region is
coupled with other electrode 274B. The p-n junction generates current
called photocurrent while light is incident and absorbed in p-n junction
276. The photo current from photodetector can be collected by the
electrode located at the top and bottom of the photodetectors 164. In
easiness in the bonding (like transmitter) as described previously, the
top electrode 274A can be taken to the bottom side of the substrate 222B
through hole electrode 276, fabricated by the process, as mentioned
previously. In the present invention, as the O-E substrate where
photodetector is bonded, is vertically located in between the chip and
optical signal propagation media, the bonding and receiving the optical
signal in accordance with this invention are preferably in both side of
the photodetector, and the illustrated detector fulfill this criteria.

[0128]FIGS. 28A and 28B are enlarged top and cross-sectional views taken
along B-B' direction of FIG. 28A for the bottom incidence type
photodetector in the preferred embodiment in accordance with the present
invention, wherein like parts are indicated by like reference numerals as
used in FIGS. 27A and 27B, so that repeated explanation is omitted here.
In the preferred embodiment, the light beam 280 is emitted to the
detector 164 from back-side of the substrate 222B, and the bonding for
electrical connections are carried out through the electrodes 282A and
282B, located at the front (top) side of the photodetector 164. The
n-doped region electrode in the case of the n-substrate, can be formed on
the front surface of the photodetector by the process consisting of, (a)
photolithography based patterning, (b) wet etching or dry etching using
ECR-RIBE, RIE, (c) formation of the insulation layer, and (d)
metallization for the cathode electrode. The bonding of this
photodetector onto the O-E board substrate 150 can be done using the
solder bump or conductive polymer bump by using the technique as
described previously.

[0129]FIGS. 29A and 29B are enlarged top and cross-sectional views taken
along B-B' direction of FIG. 28A for the bottom incidence type
photodetector in the preferred embodiment in accordance with the present
invention, wherein like parts are indicated by like reference numerals as
used in FIGS. 27A and 27B, so that repeated explanation is omitted here.
In the preferred embodiment, the microlens 286 (in FIG. 29A) is formed in
the backside of the substrate 222B, located under the anode electrode
282A of the photodetector 164B. This microlens (es) enables to enhance
the photodetector responsivity (ratio of photocurrent in Amp to optical
power in watt). This helps to eliminate the amplifier circuit, which are
either incorporating in the chip itself, or additionally including with
the photodetector. Referring to FIG. 29B, the trench 288 under the active
region (anode) is opened at the backside of the substrate 222B. This
enables to increase the responsivity of the photodetector 164C. The
trench 288 can be opened either by using the dry etching or using the
technique of the vapor-phase epitaxial lift-off, as explained in
previously. The backside of the photodetecor 164B can further be
encapsulated (not shown) by the adhesive layer with microlens located at
the trench 288, and formed using the standard microlens fabrication
technique. This enables further enhancement of the responsivity, and also
helps to increase the tolerance in assembly.

[0130]From FIGS. 27 to 29, the photodetectors illustrated can be
fabricated onto the Si for detecting the 650 nm light, GaAs for 850 nm
and 980 nm light, and InP for 1310 and above wavelength light. Also type
of photodetectors illustrated here is surface incidence type
photodetector. However, edge incidence type photodetector (not shown) in
conjunction with 45 degree mirror (beam direction opposite to edge
emitter case) can be also be used in the O-E board. Spot size converter
can also be integrated with the edge incidence photodetector. This
spot-size converter enables to increase coupling efficiency and tolerance
in assembly. In the case of electrical driver as described in emitter
(FIGS. 25 and 26), the amplifier circuit may necessary in photodetector
case to amplify the electrical signal essential to input to the chip
through the contacts in O-E board. The amplifier and photodetector can be
fabricated independently and bonded like electrical driver as illustrated
in FIGS. 25 and 26. Alternatively, the amplifier and other related
circuit such as matching circuit considering the parasitic affect due to
the solder bump, electrical contacts fabricated onto a single wafer or
can be incorporated in the driver circuit to achieve the electrical
signal in close proximity to the photodetector and receiver (amplifier).
In all illustrations, two electrodes per device are considered (to match
with the O-E board as illustrated FIGS. 6 and 7). However, each device
may have plurality of signal and/or power electrodes.

Description of the Waveguide Board, its Fabrication, and Mounting
Technique onto the PCB

[0131]FIG. 30 is a schematic plan view of a waveguide board, matching with
the O-E board as shown in FIG. 6, in the preferred embodiment according
to the invention. Each waveguide board 290 includes a singulated
substrate 292 and singulated portion of the flex waveguide optical
circuit 294. The waveguide board 290 extended from one chip to another
chip required to be interconnected with. For multichip configuration, it
may be extended to multichip. In simplicity in drawing, portion of the
waveguide board 290 in one chip's O-E board side is only shown. However,
similar board portion can be expected in another chip side also. The
waveguide board 290 and the flex optical circuit 294 have a peripheral
outline substantially similar to that of the O-E board. The flex optical
circuit 294 includes a polymer substrate 292 which is flexible material,
and can act as the under clad for the waveguide structure and also
electrically insulating. Suitable materials for this flex substrate
include the polyamide, polyester, epoxy, urethane, polystyrene, and
polycarbonate. The thickness of the substrate can be from 20 um to 500
um. The waveguide boards 290 include an array of the optical waveguide
circuit for propagating optical signal for off-chip communication, and an
array of external contacts 296 and 298 for electrical connection with the
upper O-E board 140, and lower PCB board 101, respectively. For
simplicity in FIG. 30, optical waveguide circuit 294 and external
contacts 296 (and 298) are illustrated in an array of two rows. Some
dense arrays can cover entire face of the waveguide board 290, including
thousands of the waveguide circuit for optical connection, and external
contacts for electrical connection.

[0132]FIGS. 31A and 31B are the enlarged cross-sectional views of the
waveguide board taken across A-A' and B-B' direction of FIG. 30,
illustrated in accordance with the present invention, where the same
reference numerals are the same parts, so that repeated explanation are
omitted here. The waveguide board provides the electrical connections
between top O-E board 140 and bottom PCB board 101, and also provides
optical connection on the PCB board for off-chip communication. The
waveguide board comprises substrate 292 with waveguides optical circuit
294, and the electrical contacts 296 and 298. The fabrication processes
of the waveguide board are described later. The waveguide optical circuit
294 includes the optical circuits 294A and 294B for the transmitting and
receiving the optical signals 114 (and 116 not shown in FIG. 31B) to and
from the counterpart chip. Each waveguide include two 45-degree mirrors
300 at the end to redirect the beam from vertical to horizontal
direction, and vice-versa. The electrical contacts 296 and 298 located on
the top and bottom surface of the waveguide board 290 makes electrical
connection between the O-E board 140 and PCB board 101. Electrical
connections include the power and ground connection along with and
without the low speed electrical signals, if necessary. The electrical
connections of the waveguide board 290 to the PCB board 101 can be
performed by reflowing the solder bumps 304 (and 302) on the contacts 298
(and 296) or by the pin/socket connections (explained later). Following
the mounting of the waveguide board on the PCB board, the O-E board with
the chip-package is mounted (explained later).

[0133]FIGS. 32 to 35 are the cross-sectional views showing the fabrication
processes of the waveguide board in the preferred embodiments according
to the invention. The core layer 306 is formed onto the substrate 292
using the techniques such as spin-coat, or standard deposition techniques
such as sputtering, evaporation polymerization, or vapor-phase
polymerization. Spin-coat is preferable, which makes the fabrication
process inexpensive. Other standard process can also be also used for
forming core layer 306. If the spin-coat is used for guiding layer
formation, two steps temperature curing may be used for hardening which
makes the uniform surface. The core layer 306 has the refractive index
higher than the substrate 292, essential to guide the light beam. For
waveguide core, the thickness is from 3 um to 10 um, and can be selected
based on the refractive index of the core layer 306. Photolithography
based patterning, and subsequent etching using the ECR, RIBE or milling
form the core 308 of the waveguide 294. This is followed by the formation
of the clad layer 310. The metal contacts 296 and 298 at both ends of
through-hole electrode 309, is formed top and bottom side of the
waveguide board. Each metal contacts may have the metal balls, namely
solder bumps, to help for the bonding with the PCB board 101.

[0134]Again standard photolithography based patterning, etching, and
metallization can make the electrodes 309 for external electrical
contacts 296 and 298 required for O-E board and PCB connections. Etching
for hole formation may include the process such RIE, ECR-RIBE, or
milling. Laser drilling technique can also be used for making the hole.
In this case preformed alignment marks (not shown) on the substrate 292
can be used for positioning the hole to be opened, and the alignment mark
can be formed prior to forming the core layer. Alternatively, the
photolithography based patterning for positioning can also be used for
hole formation.

[0135]To etch 312 for 45-degree mirror 300, laser drilling or direct
cutting techniques can be formed using the technique such as Laser
drilling or knife-cutting method following the photolithography based
patterning. The patterning can alternatively can be formed at the same
time of patterning formation for opening the hole for electrodes 309. For
using the laser drilling technique, excimer laser having the wavelength
1.024 μm can be used. Appropriate adjusting the power and pulse width
of the laser can make the uniform etching making smooth mirror. In the
case of laser drilling technique, either laser beam can be positioned 45
degree with respect to the substrate (placed in horizontally), or the
substrate can be inclined 45 degree with respect to the laser beam,
placed horizontally or vertically. In the case of direct cutting
technique, diamond blade can be used for etching 312, either blade or
substrate can be moved at 45 degree for cutting the portion for mirror
formation. Alternatively, 90-degree V-shaped diamond blade (not shown)
can also be used for cutting the waveguide portion. The reflectivity of
the mirror 300 can be increased by depositing the reflective metal, which
includes gold, aluminum, copper, tungsten, chromium, and platinum. These
metals can be deposited using the standard deposition techniques such as
sputtering, thermal evaporation, ion-beam evaporation, or CVD.

[0136]The substrate 292 can be a flex or a rigid substrate. If the
substrate is flex type, the substrate include all kinds of the flex
polymer, and this includes Rigid substrate includes also rigid polymer,
ceramics such as quartz glass, silicon, or polycarbonate, ethylene type
for substrate can be flex polymer including the polycarbonate, silicon
based glass. Additional underclad (not shown) above the substrate 292 may
necessary, if the substrate 292 can't be acted as the under clad for the
waveguide. The material for the under clad may include epoxy based resin
(for example, styrene etc.), deuterated-polymethylmethacrylate (d-PMMA)
or acrylate materials. The polymer material can be hardened using the
techniques including UV or heat based curing under the temperatures
varying from 100 C to 300 C. The material for core layer 306 also
includes the polymer-based material, and this includes fluorine-based
polymer, PMMA or PMMA based material. Fluorinated polymer includes the
type of material used in the plastic optical fiber, like LUCINA
(commercialized by Asahi Glass, Tokyo, Japan), and other fluorine-based
polymer also includes the polymer, OPI-N1005, and OPI-N3405,
commercialized by Hitachi Chemical Co., Tokyo, Japan. The d-PMMA with
controlling the refractive index can also be used as the core material.
The material for the upper clad 310 may include also epoxy-based polymer,
as mentioned previously. Deuterated and fluorinated polymethacrylate
(d-FPM) is also include for the clad material. It was seen that if D-PMMA
is used as the core material and d-FPM as the clad layer, the refractive
index difference (between core and clad) 1.0% could be obtained at 1310
nm and 1550 nm for single mode waveguide. Alternatively, the upper clad
310 may be omitted if the core refractive index high enough guiding the
light beams through the core layer.

[0137]FIGS. 33A to 33E are the cross-sectional views showing the
fabrication processes of the waveguide board in the preferred embodiment
according to the invention, where the same reference numerals are the
same parts, as shown in FIG. 32, so that repeated explanation are omitted
here. In the preferred embodiment, two-step metallization processes can
be used. First metallization is used to form the electrode 309, prior to
the deposition of the core layer, and the final metallization can be done
after forming the waveguide 294. The two step metallizations enable to
layout the electrode contacts 298 different from the contacts 296.

[0138]FIGS. 34A to 34E are the cross-sectional views showing the
fabrication processes of the waveguide board in the preferred embodiment
according to the invention, where the same reference numerals are the
same parts, as shown in FIG. 32, so that repeated explanation are omitted
here. In the preferred embodiment, the core layer 306B is stacked on to
the epoxy-resin 314, coated onto the substrate 292. The core layer 306B
can be a kind of polymer sheet, thickness varying from 110 μm to 500
μm, and the refractive index is higher than the epoxy resin 314 used
for bonding the polymer sheet (306B) on the substrate. This enables the
fabrication process of the waveguide board simpler, and thereby reducing
the cost. The core material includes the material types, as mentioned
previously. The polymer sheet 306B can be polished (not shown) to
adequate thickness appropriate for the core layer to guide the light
beam. For polishing, chemical mechanical polishing can be used, as
mentioned previously. The rest of the processes are similar, as mentioned
in FIGS. 32 and 33. Alternatively, the array of complete waveguides 294
with predetermined pitch (not shown here), in the form of the flex-sheet
can also be fabricated, and stacked on the flex substrate 292. Only steps
necessary in that case, are the related processes for making the contacts
296 and 298.

[0139]FIGS. 35A and 35B are the enlarged cross-sectional views in the
preferred embodiment accordance with the invention, where the same
reference numerals are the same parts, as shown in FIG. 32E, so that
repeated explanation are omitted here. In the preferred embodiment, the
microlens in form the defractive or reflective lens for either
collimating or focusing the beam are formed following the mirror and
waveguide formation. These microlens enables to increase the coupling
efficiency and tolerance required in assembly process. The microlens can
be in the form of concave type lens 316 or grating type lens 318. These
lenses can be formed independently and bonded onto the mirror using the
epoxy resin. The focal length of the microlens can be selected and
designed, as required to enhance the efficiency in coupling the beam with
the waveguide. The gap 312 formed for mirror formation can be filled by
the same epoxy resin, which is also used for bonding the discrete
microlen(es) 316 and 318. The epoxy-resin also acts as the refractive
index matched for the lens, gap and core layer. The using of the
epoxy-resin provides lower reflection loss, generally experienced while
light passes from one medium to another medium having different
refractive indices. The same type of epoxy-resin as described previously
can be used for bonding purpose. In FIGS. 35A and 35B, the explanation is
provided based on the FIG. 32E. The similar lens can also be used for the
waveguide boards, as explained in FIGS. 33E and 34E.

[0140]FIGS. 36A and 36B are the enlarged cross-sectional views in the
preferred embodiment in accordance with the invention, where the same
reference numerals are the same parts, as shown in FIGS. 35A, and 35B, so
that repeated explanation are omitted here. In the preferred embodiment,
the planar microlens 316B and 318B are formed onto the mirror using the
same polymer material as upper clad, using the standard microlens
fabrication processes technique.

[0141]FIGS. 37A to 37E are enlarged cross-sectional views showing the
fabrication process of the flex optical circuit, in the preferred
embodiment in accordance with the invention, where the same reference
numerals are the same parts, as shown in previous, so that repeated
explanation are omitted here. As the object of this invention is to
achieve inexpensive board, all components used in the optical
interconnection in the present invention are to be fabricated in simpler
and cost-effective process. In the preferred embodiments, the flex
optical circuit is fabricated which can be stacked onto the board (for
optical and electrical connections), which is easily mountable or stacked
onto the PCB. Referring to FIGS. 37A to 37E, core layer 306B, under clad
layer 314B, the epoxy-resin, and the metal layer 324 are formed onto the
substrate 322. For core layer 306B, fluorinated based polymer as
mentioned previously can be used. For clad layer, polymer based material
including PMMA based material, fluorinated based material having lower
refractive index than core, or epoxy-resin as mentioned previously, can
be used. The metal layer 324 helps for etching the substrate after the
waveguide form. The substrate 322 includes rigid substrate including Si,
SiC, and ceramics. The core 308B to guide the light beam can be
fabricated after photolithography based patterning and dry-etching using
RIE, RIBE, or milling. The formation of the upper clad 310B, and the
resin layer 326 on the top of the core form the waveguide. The 45-degree
mirror formation using the techniques as described previously makes the
waveguide with mirror to direct the light beam. After the waveguide and
mirror formation, the wet etching of substrate makes the flex optical
circuit 328, stackable onto the any substrate.

[0142]The electrode formation for external electrical connection can be
done after or before the flex optical circuit 328 stacked onto the
separate substrate 292B. FIGS. 38A and 38B are the top and
cross-sectional views of the flex-optical circuit with the underlying
substrate, taken across A-A' direction of FIG. 38A, in the preferred
embodiments in accordance with the invention, wherein the same reference
numerals indicate the same parts as mentioned in FIG. 37, so that the
repeated explanation is omitted. The flex circuit sheet 330 is stacked
onto the substrate 292B using the epoxy-resin. The electrode formations
through hole for external electrical connections are followed for
complete the waveguide formation. The substrate can be flex or rigid, as
explained before. The process is same as explained in FIG. 32D. Noted
here that the flex circuit can be designed in predetermined pitch for the
waveguide (receiving and transmitting), compatible for different
variation of the PCB layout. In the preferred embodiment, the flex
optical circuit sheet 330 is formed independently and stacks afterwards
to make the waveguide board. Alternatively, flex-optical circuit can also
be fabricated on to the 292B instead of the 322. In this case, the metal
layer may not be necessary. Alternatively, the metal layer can be used to
make two layers of the electrodes for external electrical connection,
which may reduce the size of the waveguide board.

[0143]FIGS. 39A and 39B are the top and cross-sectional views of the
flex-optical circuit with the underlying substrate, taken across A-A'
direction of FIG. 39A, in the preferred embodiments in accordance with
the invention, wherein the same reference numerals indicate the same
parts as mentioned in FIG. 38, so that the repeated explanation is
omitted. In the preferred embodiment, the electrode is formed in the flex
optical circuit 330B (flex optoelectronics circuit) prior to the wet
etching away of the substrate 322. The optoelectronics flex circuit 330B
is stacked/bonded onto the substrate 292B with electrical connection. The
bonding process can be the same as described in FIGS. 8 to 16.
Alternatively bonding using mechanical pressing can also be used for
stacking the 330B onto the 292B. This can be done using the conductive
polymer bumps which is mechanically complaint bonding. In the preferred
embodiment, the flex optical (optoelectronics) circuit sheet 330B and the
substrate with external electrical connections are made independently,
and stacked afterwards to make the waveguide board 290C. Alternatively,
flex waveguide board 290C can be made using the substrate 292B from the
beginning, instead of using the substrate 322.

[0144]FIGS. 40A and 40B are the cross-sectional views showing the mounting
of the flex optical circuit to the substrate in the preferred embodiments
according to the invention, wherein the same reference numerals indicate
the same parts as mentioned in FIGS. 38 and 39, so that the repeated
explanation is omitted here. In the preferred embodiment, the hole 332 is
opened in the flex optical circuit following the wet etching of the
substrate 322. The hole can be opened using the techniques including
laser drilling, dry etching, milling, after photolithography-based
patterning. The electrode is formed in the substrate 292B for electrical
connection. The electrode is formed in a way that the thickness is higher
than the substrate thickness leaving the portion 336 on the top of the
substrate. The electrode can be formed using the electroplating following
the photolithography based patterning leaving the photoresist portion at
the top (not shown). The thickness of the photoresist determines the
height of electrode portion 336 leaving at the top of substrate 292B. The
electrode 336 at the top enables to position the flex optical circuit
during the mounting.

[0145]FIGS. 41A to 41E are cross-sectional views showing the fabrication
process for the flex-optical circuit in the preferred embodiment
according to the invention, wherein the same reference numerals indicate
the same parts as mentioned in FIGS. 37 to 40, so that the repeated
explanation is omitted here. In the preferred embodiment, the bare fiber
338 is laying onto the epoxy-resin 326A placed onto the substrate 322
with metal layer 324. The bare fiber is the fiber coated with thin clad
layer without jacket. The thickness of the core varies from 6 μm to
100 μm, including the single-mode (step index) fiber and also the
graded-index multimode fiber. The material can be type of material used
in silica or plastic fibers. PMMA based polymer, fluorinated based
polymer include the type of material used in the plastic fiber. The bare
fiber can be available from the Boston Fiber, MA, Mitsubishi Chemical,
Corp, Tokyo, Japan, Toray Corp, Nagoya, Japan, and Ashahi Glass, Tokyo,
Japan. After the laying out the fiber, the supporting layer 310C is
formed, and polishing using the CMP is carried out thereafter for
planarization. The polishing process can be omitted, if the conformal
layer 310C can be formed and the thickness can be controlled. Following
the layer 310C formation, the mirror formation as described previously
and the protecting layer 326B are formed. The wet etching of the
substrate 322 can make the flex optical circuit 340. The stacking onto
the alternate substrate 292B and the electrode formation for the external
electrical connection follows the process, as described in FIGS. 38 and
38B, so that the related explanation is omitted here. The advantage of
using the fiber in the preferred embodiment is that the related process
as used in FIG. 37 for creating the waveguide circuit can be omitted, and
also that the commercial bare fiber with relatively low optical loss can
be used.

[0146]The fiber 338 can be laid on the predetermined position (not shown),
after making the pattern using the standard photolithography technique.
Alternatively, the position of the fiber to be laid on the layer 326 can
also be made after making the curved (round-shaped) trenches 342 using
the master 344, as shown in FIGS. 42A and 42B. The master 344 has the
curved surfaces 346, equivalent to the surface of the bare fiber 338, and
can be made in accordance with the layout of the fiber. The fiber 338 can
be laid according to the trenches 342 onto the layer 326. The master can
be a metal and can be made using the electroplating deposition.

[0147]FIGS. 43A to 43E are cross-sectional views showing the alternative
fabrication process for the flex-optical circuit in the preferred
embodiment according to the invention, wherein the same reference
numerals indicate the same parts as mentioned in FIGS. 37 to 40, so that
the repeated explanation is omitted here. In the preferred embodiment,
the waveguide flex sheet is fabricated using the simple molding
technology, as illustrated in FIGS. 43A to 43E. After opening the grooves
342B into 322C polymer substrate using the master 344B, the grooves 342B
are filled with the precursor (UV-curable acryle resin) 348 for the core,
by injecting 322C polymer into the waveguide grooves 342B. The depth of
the grooves 342B is equal to the core thickness, and it includes from 5
um to 25 um based on the refractive index of the polymer filling up the
grooves 342B. Then the excess core material is just scraped off from the
surface by using the sliding means 352 such as squeegee in one direction
354. The cure material then exposed to the UV exposure (not shown) to
hardening material, which take out the moisture inside the core material,
and make the core 350. The precursor (UV curable acryl resin) for the
upper clad 356 is covered on to the surface using the spin coating, and
cured by UV radiation. This process will make the waveguide on the
substrate. Noted here that polymer used for the core material must have
the refractive index higher than the substrate 322C.

[0148]The master waveguide mold 344B used in FIG. 43, can be made as
illustrated in FIGS. 44A to 44E. A photoresist 360 for UV radiation are
coated on the substrate 358 for example glass substrate. The thickness of
the photoresist determines the depth of the grooves in the patterned
substrate. This is equal to the core thickness of the optical waveguide,
and it includes from 5 μm to 25 μm based on the refractive index of
the core material, as mentioned earlier. The substrate was exposed to the
UV radiation through a mask 359 on which the required waveguide pattern
362 can be made, and developed for the pattern for the photoresist. The
positive and negative resist can be used for this purpose, and the
opposite pattern can be used for this purpose. Next metallic pattern 364
can be electroplated to make the waveguide mold. The metallic plate 344B
used as the waveguide mold.

[0149]Alternatively, the waveguide could be fabricated also onto special
substrate and only waveguide portion (sheet) can be transferred to the
PCB board. The transfer can be possible using any kind of treatment, such
as the heat treatment or radiation such as UV etc. The substrate and
waveguide material must have the property of high sticking coefficient at
the room temperature, but the low sticking coefficient under certain
treatment.

[0150]FIGS. 45A to 45C are the schematics showing the structure of
transferable waveguide (to the PCB) in the preferred embodiment, wherein
the same numerals represent the same parts as mentioned in earlier. The
waveguide core 308D with upper clad 310D can be fabricated using the
technique as mentioned previously. The mirror 312B in this case also can
also be made using the technique of knife cutting or laser drilling
techniques. The difference of the mirror in this case as compared with
previous waveguide, is that the direction of the mirror is opposite so
that when it transferred to the PCB, the mirror becomes 45 degree mirror
to redirect the light in vertical direction. FIGS. 46A and 46B are the
schematics showing the transfer technique of the waveguide from the
substrate 292D to the PCB 101. Once the waveguide is transferred to the
PCB, it becomes the same waveguide as shown in previously. Noted that,
the electrical connection through conductor (not shown here) from the
chip-package to the PCB 101 is possible through the O-E board directly
bonded to the PCB. The socket can be made for this purpose. The advantage
of the transferable waveguide is that, the PCB board can be designed as
conventional way, and the waveguide portion is only left as determined.
As the waveguide is transferred to the PCB, the waveguide area (portion)
on the PCB can also be used for electrical wiring.

[0151]A layer 326D can also be used on the substrate prior to formation of
the waveguide layers. FIGS. 47 and 48 show the schematics in the
preferred embodiments wherein the same numeral represent the same parts
as shown in FIGS. 45 and 46, so that repeated explanation is omitted
here. The layer 326D acts as three folds; (a) to prevent the waveguide
from the damage while transferring to the PCB, (b) after transferring,
the layer 326D acts as the upper cladding layer, and (c) also acts as the
protecting layer to prevent the waveguide core from post-damaging.

[0152]Further grating 366 and the micro-lens 368 can also be formed on the
layer 326D to focus the beams onto the mirror. In this case also, the
mirror designed in a such a way that after transferred the waveguide to
the PCB, the lens or grating can able to focus the beam (to focus to the
mirror to transmit through the waveguide core in the case of the
receiving beam or to focus to the detector in the case of the transmitted
beam). FIGS. 49, 50, 51, and 52 show the schematics in the preferred
embodiments wherein the same numerals represent the same parts as shown
in FIGS. 45 to 48, so that repeated explanation is omitted here.

[0153]FIGS. 53A and 53B are the schematic showing the waveguide on the PCB
in the preferred embodiment wherein the same numerals represent the same
parts as shown in FIGS. 45 to 52, so that the repeated explanation is
omitted here. The waveguide 370 or 372 are placed on the PCB 101, and the
electrical connection for the low speed signals to communicate the
chip-package to the PCB are occurred through the electrodes 296B, which
is connected to the O-E board.

[0154]FIGS. 54A, 54B, and 54C are the simplified cross-sectional view of
the structure including the chip-package 120A, O-E board 140A, and
underlying PCB 101 (A) according to the present invention. For simplicity
in the explanation, one side of the chip is considered, similar
interconnects could be assumed for counterpart chip. Chip package using
of BGA or fine BGA is considered. Discrete optical components 162 (and
164), and the array of the optical components 170 (and 172) are
considered in the interconnects of FIGS. 54A and 54B, respectively.

[0155]FIGS. 55A and 55B are the simplified cross-sectional view of the
structure including the chip-package 120A, O-E board 140A, and underlying
PCB 101 (A) according to the present invention. For simplicity in the
explanation, one side of the chip is considered, similar interconnects
could be assumed for counterpart chip. Chip package using of BGA or fine
BGA is considered. The array of the optical components 170 (and 172) and
the drivers 374 is connected each other through interconnects 376. The
driver 374 and the optical components 170 (or 172) can be directly
mounted on the O-E substrate (FIG. 55A) or they can be mounted on the
common carrier 378 (FIG. 55B) before mounting on the O-E substrate.

[0156]FIGS. 56A, 56B, and 56C are the simplified cross-sectional view of
the structure including the CSP based chip-package 120A, O-E board 140A,
and underlying PCB 101 (A) according to the present invention. For
simplicity in the explanation, one side of the chip is considered,
similar interconnects could be assumed for counterpart chip. Chip package
using of BGA or fine BGA is considered. The packaged chip 120A connect
with the O-E board through the interconnects 380 and 382.

[0157]FIGS. 57A and 57B are the simplified cross-sectional view of the
structure including the chip-package 120A, O-E board 140A, and underlying
PCB 101 (A) according to the present invention. For simplicity in the
explanation, one side of the chip is considered, similar interconnects
could be assumed for counterpart chip. Chip package using of BGA or fine
BGA is considered. The array of the optical components 170 (and 172) and
the drivers 374 is connected each other through interconnects 376. The
driver 374 and the optical components 170 (or 172) can be directly
mounted on the O-E substrate (FIG. 57A) or they can be mounted on the
common carrier 378 (FIG. 57B) before mounting on the O-E substrate.

[0158]In the preferred embodiments, the optical components 170 (or 172)
are mounted directly on the O-E substrate or the common carrier 378. In
the high speed interconnects, an additional circuit or matching circuit
(not shown) may necessary to eliminate the parasitic effect induced due
to the interconnects such as chip-packaged and O-E board, and also O-E
board to PCB board. Using of this matching circuit, data speed as high as
10 Gb/s and beyond can be transmitted from chip packaged to other chip
without signal distortion.

[0159]The present invention has been described above by way of its
embodiments. However, those skilled in the art can reach various changes
and modifications within the scope of the idea of the present invention.
Therefore it is to be understood that those changes and modifications
also belong to the range of this invention. For example, the present
invention can be variously changed without departing from the gist of the
invention, as indicated below.

[0160]In the preferred embodiments, all contacts of the chip (with
package) are transferred to the O-E board so that the electrical contacts
for the signal lines are arranged in convenient to bonding of the optical
components in single discrete form or in array form and whereas other
ground and power lines are arranged to pass throughout the O-E board.

[0161]In the preferred embodiments, for simplicity of drawing, the
chip-scale package or fine ball grid array type packaging is considered
for the electronics chips to be interconnected. The present inventions
also cover all kinds of the package available today and also in future.
Furthermore, two contacts for each optical component are considered in
simplicity of drawings. However, the number of bonding pads on the O-E
board for optical components bonding can be varied based on the necessity
of the devices and its integration.

[0162]Although the invention has been described with respect to specific
embodiment for complete and clear disclosure, the appended claims are not
to be thus limited but are to be construed as embodying all modification
and alternative constructions that may be occurred to one skilled in the
art which fairly fall within the basic teaching here is set forth.

[0163]As the low speed signal lines (metal lines) passes from
packaged-chip to the PCB, the substantial amount of heat can able to make
dissipated through these low speed signal lines, hence no cooler use or
cost-effective cooler use is possible.

[0164]According to this present invention, z-axis of the electronics-chip
to be interconnected with other electronics chip has not been used. So
that the z-axis can be used for cooling purpose if necessary.

[0165]The present invention is expected to be found practically use in the
high-speed off-chip interconnects where the signal speed is 10 Gb/s or
beyond. The application includes high-speed multichip module
interconnection, 3-D chip or memory interconnection, high speed parallel
system for computing, gaming and graphics systems for high speed 2-D or
3-D video transmission, and high bandwidth image display, high speed
router where high speed electronics switches (or network processors) are
needed to interconnect.